The present invention relates to an article of manufacture used to alter the electrical attributes of a substrate surface upon which it is affixed.
Conventional R-cards (i.e., resistive or conductive ink printed cards) have been fabricated by screen printing an ink having electric altering properties imparted by resistive or conductive ingredients onto a major surface of a carrier, and thereafter the ink printed carrier is bonded to a part using a separate intervening adhesive coating. However, this prior approach has been implemented using a flat, relatively stiff, cured substrate carrier to print upon. For example, one approach has been to print the ink on a cured epoxy-glass laminate and then subsequently use separate film adhesive material to bond such an R-card to a part. Such an approach increased costs and labor, e.g., due to the adhesive coat operation. Also, the use of a rigid backing as a carrier for the screen printed ink has the drawback that many parts needing electrical field modulation have three dimensional exterior contours and are not flat-surfaced to facilitate interfacial contact with an adhesive coated surface of a rigid carrier for the screen printed ink.
Also, in applications where complex electronic circuits are used, the electronic noise generated by such circuits, i.e., the radio frequency/electromagnetic interference, may be of such level as to be hazardous or detrimental to nearby personnel or other electronic circuits. If such electronic noise reaches a high level, a unit may be in violation of federal regulations or the manufacturer's design specifications, requiring the unit to be recalled by the manufacturer.
One solution to the above problem, is to redesign the circuit components per se to reduce RFI and EMI to acceptable levels. However, this is a costly remedy. It has also been proposed that a foil shield be placed around the electronic circuitry and connected to ground as another viable approach to reducing environmental radiation from electronic circuitry. Towards this end, an aluminum or copper foil has been adhesively coated on both sides of a substrate, and an outer wrapping layer of polyester or plastics material has been applied thereto. However, these metal foil shielding arrangements are relatively costly and are not especially durable.
Also in the prior art, it is known to reduce EMI within a microwave module by producing a sheet of absorber material, such as an elastomer material filled with iron powder, cutting out a pattern from the sheet of absorber material to fit around the components within the module (this pattern generally being relatively complex in shape), and then bonding the absorber to the module lid with an adhesive. However, the precision shaping and positioning required of the sheet of absorber material significantly increase costs. In an effort to lower these costs, it also has been previously proposed to directly form a screen printed microwave absorbing material on microwave module lids, such as by dispersion of a microwave absorbing material like powdered iron or ferrite particles in a thermosetting liquid resin, and curing the ink, to suppress EMI. While such direct screen printing approaches may be useful for flat, two-dimensional substrates, it is not particularly practical for implementation on three-dimensional substrates of complex surface geometries.